There has been an ever increasing concern with limiting loss of life and damage to property from fires, both in connection with transportation and in stationary facilities.
In connection with rail transportation, for example, the Transportation Systems Center of the U.S. Department of Transportation developed proposed Guidelines for flame spread and smoke density, as measured by ASTM E-162 and E662, respectively, for all interior materials in fixed guideway vehicles. In the years since these standards were proposed, there has been improvement in the safety performance of such interior materials.
Two areas, however, were left without standards. There were no established standards to limit the amount of toxic off-gases and the standards permitted the acceptance of combustible materials which contributed significant fuel to fires. As a result, some products that conformed to the guidelines were nevertheless not totally satisfactory in a practical sense.
One material, which has been used for several years as a fire retardant material, is a silicone rubber foam that is a reaction product of a vinyl-terminated polysiloxane containing --Si(CH.sub.3).sub.2 O-- units and an organohydrogen siloxane polymer containing --Si(H)(CH.sub.3)O-- units. This material has demonstrated good fire retardance and excellent weatherability, aging and durability properties and could be formulated to be a low emitter of toxic gases under fire conditions. Its fire retardance, however, is not good enough to meet the guidelines of the mass transit industry which require a flame spread index not greater than 25 when tested in accordance with ASTM E-162.